1. Field of the Invention
The present invention relates in general to a filling apparatus, and more particularly to a liquid filling apparatus applicable to a canning machine or the like.
2. Description of the Prior Art
At first, a filling machine in the prior art, which is disclosed in Japanese Patent Application No. 1-55185 (1989), will be described with reference to FIG. 9. In this figure, gas switching valve main bodies 953 are fixedly secured at predetermined intervals to a bottom of an annular tank 932 for accommodating liquid by means of bolts 954, and on the bottom surface of the gas switching valve main body 953 is a housing 901 fixedly secured to the former by means of bolts 955. Liquid to fill a container 934 is subjected to gas pressure while occupying an inner space 933 of the aforementioned annular tank 932. The surface of the liquid is held lower than the upper level of the available inner space 933 of the annular tank 932 so that a space for gas extends above the surface. On the outside of the housing 901 is slidably mounted a holding cylinder 904 which is formed as a hollow cylinder and serves to position and seal a container 934. The holding member 904 is held in tight contact with the outer surface of the housing 901 at a location indicated by reference numeral 935, and on its central side surface portion, it has a recess 936 which is adapted to receive a fork-shaped tool (not shown) for vertically moving this holding member 904 with respect to the housing 901. The holding member 904 is provided with a positioning conical portion 937 defining a tapered opening extending inwardly from its bottom end. At the inner end portion of this positioning conical portion 937 is disposed a sealing element 938 serving as a seal member for the container 934.
The container 934 is placed on a lower support table 939 fixed to the housing 901, and it is constrained at a position centered with respect to the filling apparatus by means of a semi-circular guide section 940.
The housing 901 has an inner piece 941 at its interior, and between the inner piece 941 and an outer portion of the housing 901 is formed a nearly annular liquid feed passageway 942. An injection port 926 is provided at the bottom of the liquid feed passageway 942, and a liquid jet flow is led from the injection port 926 to an inner wall surface of the container 934, where the liquid flows toward the bottom of the container in as much of a laminar flow as is possible. The housing 901 has a stepped portion 943 defined on its inside surface, and this also defines an upper end of the inner piece 941.
The liquid feed passageway 942 terminates here, and since this passageway must be sealed here, an annular liquid valve 944 is disposed above this stepped portion 943, and this annular liquid valve 944 can be vertically moved by a pipe 946.
On the outside of the upper portion of the pipe 946 is disposed a compression spring (not shown). An inner space and an outer space 950 defined inwardly and outwardly of the pipe 946, respectively, communicate with the inner space 933 of the annular tank 932 via holes 945. On the inside of the inner piece 941 is disposed a gas pipe 951. A stepped portion 951a is provided at the top end portion of the gas pipe 951, a flange 951b is provided at a lower portion thereof, and a stopper piece 970 is fixed by a retaining ring 971 on the inside of the inner piece 941 proximate the center thereof to serve as a positioning member for the gas pipe 951. On the other hand, on the outside of the gas pipe 951 is disposed a spring 972. The bottom end of the spring 972 is fitted and secured to the upper surface of the flange 951b of the gas pipe 951, its top end butts against the stopper piece 970, and thus the spring 972 normally biases the gas pipe 951 in the downward direction.
A free end portion 986 of a bend member 985 is fitted around the gas pipe 951 without being fixedly secured thereto. The bend member 985 has one arm 989 connected to the holding member 904 by means of a pin 925 and a nut 924.
An upper surface 987 of the free end portion 986 of the bend member 985 and a lower surface of the gas pipe flange 951b are disposed with a predetermined gap S maintained therebetween.
The gas pipe 951 extends to the space 957 within the gas passageway 956, and this gas passageway extends upwards to the gas space in the annular tank 932 defined above of the liquid surface, whereby the inside of the gas pipe 951 communicates with the gas space defined within the annular tank 932. Within the gas passageway 956 is disposed a gas valve (not shown). Between the outer surface of the housing 901 and the inner surface of the holding member 904 is provided an annular chamber 959. This annular chamber 959 communicates via a passageway 962 with a release valve 961 which can be opened externally by means of a tappet 960, and the annular chamber 959 communicates via a passageway 963 with the interior of the sealing element 938.
The above-described filling apparatus in the prior art gives rise to the following problems.
That is, since the spring 972 for biasing the gas pipe 951 downwards is provided between the flange 951 at the lower portion of the gas pipe and the stopper piece 970 fixedly secured to the housing inner piece 941, when the container 934 is taken out from the filling apparatus, a compression length of the above-mentioned spring 972 at the time of raising the holding member 901 upwards and elevating the lower surface of the above-described gas pipe 951 up to a desired level with respect to the edge of the open end of the container 934, would correspond to a "stroke-S" of raising the aforementioned holding member. For instance, a compression length of 20-25 mm would become necessary. While a spring usable over such a large compression stroke can be manufactured in the case of a large opening diameter of a container because the inner diameter of the housing inner piece 941 is large, in the case of a filling apparatus for a container having a small opening diameter, a spring usable over the above-described large compression stroke would be impossible to manufacture.
Also, in the above-described filling apparatus in the prior art, the stepped portion 951a of the gas pipe 951 is restrained from moving downwards by the stopped piece 970 and the retaining ring 971 on the inside portion of the inner piece 941. Consequently, when the gas pipe 951 is to be replaced, the retaining ring 971 must be removed by inserting a special tool into a narrow space between the inside portion of the inner piece 941 and the outer circumference of the spring 972. This work takes a lot of time.